1. Field of the Invention
This invention relates to a chemically amplified resist composition, a process for manufacturing a semiconductor device and a patterning process.
2. Description of the Prior Art
As a device has become more compact and more accelerated, lithography using a short-wavelength light source has been employed because of improving resolution. In addition, there has been used a chemically amplified resist as a resist material.
Furthermore, the needs for size reduction and acceleration in a semiconductor device require using, besides a copper (Cu) interconnection, a so-called low dielectric constant material. A copper interconnection is generally formed by a damascene process in which a trench for an interconnection is formed on an insulating film between interconnections, the trench is filled with copper and then excessive copper in an unwanted area outside the interconnection trench is removed by chemical mechanical polishing (CMP).
There will be described formation of a copper interconnection by a damascene process using a chemically amplified resist. FIG. 10 is process cross-sections showing the procedure of a dual damascene process where a via-hole and an interconnection trench are simultaneously filled. A process where the interconnection and the via are formed by a so-called via-first process.
First, on a lower interconnection layer 108 are sequentially deposited a first etching stopper film 107, a first interlayer insulating film 106, a second etching stopper film 105, a second interlayer insulating film 104 and a third interlayer insulating film 103. Then, using well-known lithography and etching technique, a via-hole 111 is formed in the third interlayer insulating film 103, the second interlayer insulating film 104, the second etching stopper film 105 and the first interlayer insulating film 106 (FIG. 10(a)).
Then, an anti-reflection film 102 is formed on the third interlayer insulating film 103 and the first etching stopper film 107, during which the via-hole 111 is partly or totally buried with the anti-reflection film 102. This figure shows that the via-hole 111 is partly buried with the anti-reflection film 102 (FIG. 10(b)).
Next, on the anti-reflection film 102 is applied a chemically amplified resist 201 (FIG. 10(c)). Then, in the chemically amplified resist 201 is formed an opening pattern 112 for forming an interconnection trench connected to the via-hole 111 (FIG. 10(d)).
Subsequently, using the chemically amplified resist 201 as a mask, the anti-reflection film 102 on the third interlayer insulating film 103, and then the third interlayer insulating film 103 and the second interlayer insulating film 104 are etched off to form an interconnection trench 113 (FIGS. 10(e) and (f)).
Then, the chemically amplified resist 201 and the anti-reflection film 102 are stripped off by O2 plasma ashing and using an organic stripper. Next, the first etching stopper film 107 at the bottom of the via-hole 111 is etched off to provide a structure where the via-hole 111 is connected to the upper surface of the interconnection (not shown) in the lower interconnection layer 108 (FIG. 10(g)).
Next, a metal film is formed such that it buries the interconnection trench 113 and the via-hole 111. The metal film can be formed by first forming a barrier metal film within the interconnection trench 113 and the via-hole 111 by sputtering and then burying the interconnection trench 113 and the via-hole 111 with an interconnection metal film by, for example, electroplating. Subsequently, unwanted barrier metal and interconnection metal films outside the interconnection trench 113 are removed by CMP to form an interconnection 109 (FIG. 10(h)).
In such a via-first process, defective resolution of the resist on the via-hole 111 tends to occur during forming the opening pattern 112 in the chemically amplified resist 201. Such a phenomenon that defective resolution is induced in a particular area not due to a lower optical resolution, but due to an external factor inhibiting resolution of a chemically amplified resist is called “resist poisoning”. If resist poisoning occurs, an interlayer insulating film cannot be processed into a desired shape. Furthermore, when directly forming an interconnection, interconnection-defects such as stress-migration and electro-migration may occur, leading to a less reliable semiconductor device.
To solve the problem, it has been proposed that a resist composition comprising an organic base is used for preventing resist poisoning of a resist pattern (Tokkai2000-137328). Tokkai2000-137328 has described that addition of an organic base is effective for preventing dimensional fluctuation of a resist pattern because diffusion or activity of an acid after exposure is inhibited. Hereinafter, an organic base used for such a purpose is referred to as a “quencher”.
However, when adding a quencher to a resist composition, it is effective for preventing resist poisoning during resist patterning, but it may lead to deteriorate in resist sensitivity. A resist with excessively lower sensitivity may reduce a throughput in an exposure process and thus may sometimes lead to significantly deteriorated mass productivity. For example, a three-fold amount of the quencher requires an almost three-fold exposure time. Thus, when adding a sufficient amount of the quencher to completely prevent poisoning, an exposure time frequently exceed a permissible limit. Furthermore, in a lithography process with a lower throughput such as EB direct-drawing lithography, it is difficult to increase the amount of the quencher for preventing resist poisoning. Thus, the process cannot be sometimes employed due to resist poisoning.
In view of the situation, an objective of this invention is to provide a technique for preventing occurrence of poisoning and deterioration in sensitivity in a chemically amplified resist.
We have intensely investigated the above problems, conducting extensive experiments, and consequently have found the followings.
In a via-first process described above with reference to FIG. 10, it has been found that sensitivity in a chemically amplified resist may be lowered because of the mechanism described below. FIG. 11 is a process cross-section showing occurrence of defective formation of a chemically amplified resist on a via-hole.
First, by the above steps illustrated in FIGS. 10(a) to 10(c), a chemically amplified resist 201 is applied on an anti-reflection film 102. Then, an opening pattern 112 for forming an interconnection trench is transferred to the chemically amplified resist 201. In the process, as shown in FIG. 11(a), a chemically amplified resist 201 cannot be removed on and around the upper surface of the via-hole and partly remains (FIG. 11(a)).
Then, the anti-reflection film 102 is removed (FIG. 11(b)), and then the third interlayer insulating film 103 and the second interlayer insulating film 104 are etched off (FIG. 11(c)). In the process, as shown in FIG. 11(a), the chemically amplified resist 201 remains within the opening pattern 112, so that an interconnection trench 113 is not formed in conformity to a pattern and a residual fence 114 of the third interlayer insulating film 103 and the second interlayer insulating film 104 is formed on and around the upper surface of the via-hole. The residual fence 114 is not removed by subsequent O2 plasma ashing or treatment with an organic stripper (FIG. 11(d)), and remains in the interconnection trench 113 (FIG. 11(e)).
We have further analyzed the cause of a defective pattern in the above process and have obtained a new finding described below. Specifically, it has been found that an amine or its analogue is formed in an interlayer insulating film formed on a semiconductor substrate and the compound is subjected to neutralization with an acid catalyst in a chemically amplified resist, leading to deteriorated sensitivity of a resist.
A variety of sources may be deduced for such an amine; for example, a nitrogen-containing film formed under a resist, NOx in a deposition gas used for, e. g., depositing a silicon oxide film, or an amine present in a stripper used for removing a resist.